1. Field of the Invention
The present invention relates to echo cancellation in an electronic device such as a portable phone enabling handsfree calls and particularly relates to an electronic device that performs echo suppression interlocked with received voice volume, an echo canceling method thereof, an echo canceling program thereof, a recording medium, a circuit substrate, and a portable telephone terminal device.
2. Description of the Related Art
In an electronic device having a short distance between a microphone and a speaker, such as a miniaturized portable phone, output voice (received voice) of the speaker sneaks into the microphone and is transmitted as transmission voice. Especially, in the case of a telephone with a handsfree call function, a large amount of output voice (received voice) of the speaker sneaks into the microphone, and the transmission voice is returned through a telephone of a phone call destination, sneaks into a microphone, and is transmitted again, resulting in echo. Such echo disturbs a voice call through deterioration of intelligibility etc., and makes callers uncomfortable.
With regard to a measure for alleviating the echo due to the received voice sneaking into the transmission voice, Japanese Patent Application Laid-Open Publication No. S62 (1987)-163427 discloses that a pseudo echo signal is generated in response to a received signal (received voice) to subtract the pseudo echo signal from a transmitted signal (transmitted voice), that an echo canceller uses a received signal passing through a level varying means that adjusts the speaker volume, etc. Japanese Patent Application Laid-Open Publication No. H05 (1993)-022392 discloses that surrounding noise is collected and that the surrounding noise signal is used for arithmetically processing and removing a surrounding noise signal included in a transmitted voice signal.
By the way, when echo cancellation is performed with the process disclosed in Japanese Patent Application Laid-Open Publication No. S62(1987)-163427, i.e., by generating a pseudo echo signal in response to a received signal (received voice) to subtract the pseudo echo signal from a transmitted signal (transmitted voice), if the echo canceller capability is low in a telephone of a phone call destination or if the level of the transmitted voice is high, a loop gain exceeds 0 [dB] and howling may be generated due to an echo signal.
Although echo suppression may be performed in accordance with the level of the received voice to suppress generation of the howling, since echo suppression function works in the two-way phone call outputting the received voice and inputting the transmitted voice, the voice arriving at the phone call destination is extremely attenuated, and therefore, it feels difficult to here the voice.
Since enhancement of the echo suppression disturbs the function of the two-way phone call and mitigation of the echo suppression reduces the echo suppression effect, delicate adjustment of parameters is necessary for balancing both enhancement and mitigation. Since the echo amount is fluctuated by the voice volume adjustment on the receiver side, parameters must be adjusted on the basis of the received voice volume. Therefore, the echo must be suppressed without impairing the original phone call function such as two-way phone calls.
In Japanese Patent Application Laid-Open Publication Nos. S62 (1987)-163427 and H05 (1993)-022392, such problems are not disclosed, and a solving means thereof is not disclosed or indicated.